invention relates generally to apparatus for grading or sorting solid objects and more particularly to grading apparatus having gauging passages between a tilted bed and a set of parallel grading rollers obliquely arranged across the bed.
Tilted graders having oblique grading rollers are used to sort objects into different sizes, or grades. Solid objects that are graded include food products such as fruits, vegetables, nuts, shellfish, portions of meat, poultry, and fish, and non-food products, such as bearings, castings, and aggregates. One kind of grader often used to grade shellfish, such as raw shrimp, comprises a grading bed tilted from a higher upstream end to a lower downstream end. Shrimp are fed onto the bed at its higher upstream end. Aided by gravity and water, the shrimp slide down the declining bed. Parallel grading rollers extend obliquely across the width of the bed. The rollers are separated from the bed by gaps, which are successively smaller from the upstream-most grading roller to the downstream-most roller. The gaps define consecutive gauging passages. Shrimp too large to fit through the gap at a grading roller are augered along the obliquely arranged roller by a helical ridge on the roller's periphery and dropped off the side of the grader into a container or onto a conveyor. The smaller shrimp pass under the grading roller to the next grading roller, whose gap is smaller. Thus, each roller sorts shrimp of a certain grade off the side of the grader.
For accurate grading, the grading bed, which is typically a sheet of metal, should have a flat upper surface without bumps and dips, especially in the vicinity of the grading rollers, to maintain a uniform gap along the entire length of each grading roller.